1. Field of the Invention
The present invention relates to systems and method for improving water quality, and, more particularly, to such systems and methods for bioremediating water with an attached algal colony, and, most particularly, to treating water against undesired toxins, microorganisms, and other water-borne pollutants in concert with an attached algal colony.
2. Description of Related Art
Algae comprise a group of plants, existing in approximately 18,000 different species, whose primary nutrients include carbon, nitrogen, and phosphorus, as well as a suite of micronutrients essential to plant growth.
The removal of contaminants from wastewater and ground water has become an important problem in restoring ecological balance to polluted areas. It is known that some algal species are capable of absorbing heavy metals into their cell walls, thus reducing their toxic effects on the environment. Algae can also take up nutrients and micronutrients that may be present in overabundance, such as phosphorus, potassium, nitrogen, iron, aluminum, and calcium, and can thus be utilized to remediate an ecosystem. Such remediation can occur when water flows over stationary algae, also absorbing carbon dioxide and releasing oxygen in the process as a result of respiration and photosynthesis. Further, the water passing over the PF experiences an increase in pH owing to the removal of carbon. The filtration can occur through adsorption, absorption, physical trapping, and other more complex means.
A system used to effect this uptake is known as a periphyton filter, the periphyton comprising a culture of a family of fresh, brackish, and/or salt-water aquatic plants known as attached microalgae. Unlike such organisms as free-floating plankton, benthos or attached algae is stationary community of epiphytes that will grow on a wide variety of surfaces. When occurring in the path of flowing water, the stationary algae remove nutrients and other compounds from the passing water, while absorbing CO2 and releasing O2 as a result of respiration and photosynthesis. Once a colony is established, roots or holdfasts cover the culture surface. If the plant bodies are harvested, leaving the roots behind, the nutrients and other pollutants contained in the plant bodies are removed from the water, causing a natural filtration effect.
A further advantage to this technique is that the enriched algae can be harvested and used as fish or animal feed, which serves to return the nutrients to the food chain.
Periphyton filters (PF) have the potential for use in a variety of applications. For example, the turf can be used to replace biological or bacteriological filters in aquaria. As mentioned, natural periphyton can be used to remove nutrients and other contaminants from polluted waters. In addition, by harvesting the algal mass, various processes can be used to produce a biomass energy source such as methane or ethanol, fertilizer, a human or animal food additive or supplement, cosmetics, or pharmaceuticals.
The high productivity of the algae in a fibrous form has also yielded uses in the paper and paper products industry, as the harvested algae are stronger and easier to process than wood fiber. This capability has resulted in a sustainable method of managing human impact on aquatic ecosystems.
Periphyton filters behave differently in water with varying location, speciation, chemical characteristics, and other parameters. Experience in situ has in some cases resulted in weak or poor productivity owing to low concentrations of available nutrients. It has been shown that if a fraction of the primary nutrients are not available, then the periphyton filters struggle to develop the critical mass necessary to invoke a substantial precipitation and physical trapping capability and concurrent filtration characteristics. In particular, the presence of microinvertebrates and their eggs can compromise the success of a periphyton filtration system by consuming desirable periphyton and by eating the root or holdfast of the algal filament.
Toxic cyanobacteria pose a particularly formidable set of filtration challenges in that the toxins are very persistent in the environment and can exist both inside and outside the algal cell. It is known to treat toxin-containing water with ozone because of its strong oxidizing effect when mixed in water; however, the nutrients in ozonated water become available and are reconsumed by the toxic algae.
Studies in algal turf production are known in the art. Algal turf techniques have been disclosed in Adey's U.S. Pat. No. 4,333,263, and the present inventor's U.S. Pat. Nos. 5,131,820, 5,527,456, 5,573,669, 5,591,341, 5,846,423, and 5,985,147, the disclosures of which are incorporated herein by reference.